1. Field of the Invention
The present invention relates to a method of providing a glass tube to be used in tubular gas-gas heat exchangers with a glass spiral on the inside wall of the tube in order to increase the heat transfer efficiency of the heat exchanger.
2. Description of the Related Art
A glass tube for use in heat exchangers has an inside diameter, ID, of typically about 25-60 mm. The diameter of the spiralized glass rod or thread is typically about 1-12 mm. The spiral is fully or partly melted on to the inside glass wall and has a pitch height of typically 2-10 times of the ID. The glass tube can have lengths of up to 250 times of the ID, and its wall thickness is typically 5 to 8% of the ID.